This Core Unit has two primary functions. One function of this Core Unit is to analyze plasma, tissue, and intestinal lumen samples for lipid concentration and composition, and to size micelles and vesicles. This Core Unit will also function as a source of expertise in a variety of studies of mice, in vivo rates of sterol synthesis in hamsters and mice, and LDL uptake rates in hamsters. Due to the types of analyses being completed, this Core will serve all projects in a highly interactive and collaborative manner. The first function of this Core is to analyze lipid concentration and content of different types of samples generated from humans and animals. Plasma total and LDL cholesterol concentrations will be determined by standardized techniques. Postprandial samples from intestinal lumen of both animals and humans will be assayed for cholesterol solubility, micellar and vesicular size, bile acid composition and concentration, cholesterol concentration, phospholipid concentration and glyceride concentration. The second function of this Core utilizes the expertise of the lead and participating investigators. Cholesterol and triglyceride absorption, as determined by secretion of radiolabeled lipid into lymph, will be measured in this Core in mice lacking various digestive enzymes. In addition, this ore will study sterol balance across mice lacking the same digestive enzymes by measuring in vivo rates of synthesis in the liver, small intestine and remaining carcass. Finally, in vivo sterol synthesis rates and LDL-cholesterol uptake rates will be determined in hamsters fed diets similar to human if the various diets resulted in changes in sterol fractional synthetic rates, LDL-cholesterol levels or mRNA levels for HMG-CoA reductase or the LDL receptor.